Which active pitchers are most likely to reach 4,000 career strikeouts?

On August 22, 1989, Nolan Ryan fanned Rickey Henderson to record the 5,000th strikeout of his big league career. The Hall of Famer would retire four years later with an astounding 5,714 whiffs -- most all-time and 839 K's ahead Randy Johnson's second-place total (4,875). The only other pitchers to reach even the 4,000 mark are Roger Clemens (4,672) and Steve Carlton (4,136).

With a five-man pitching rotation and today's limited pitch counts, it's almost unthinkable that we'll see another 5,000-K career -- unless Bartolo Colon pitches for another 20 years, which is certainly possible. So let's take a look at current pitchers who could potentially join the 4,000-K Club.

The active leader: CC Sabathia (34 years old, 2,437 strikeouts)

Carlton finshed his age-34 season with 2,683 career strikeouts and Johnson had only 2,329 at that point, so Sabathia is in the ballpark. Longevity is a major factor, however, and CC made just eight starts this season after posting the highest ERA of his career in 2013. The big lefty is signed through 2017 in New York, so he'll have plenty of opportunity to keep racking up K's into his late 30's if he can remain healthy enough to take the mound.

The next contender: Felix Hernandez (28 years old, 1,900 strikeouts)

Barring an injury, King Felix will finish his age-28 season with about 1,950 career K's. Since 1900, only Sam McDowell, Walter Johnson and Bert Blyleven have whiffed 1,950 batters through the same age. Respective totals for Ryan, Johnson, Clemens and Carlton at that point: 1,758, 818, 1,665 and 1,484. Hernandez pitched his first full season at age 20 and has barely missed a start since. He's whiffed at least 200 hitters every year since '09 and is on pace to set a new high in K/9 rate for the fifth consecutive campaign. Felix has a lot going for him: youth, durability, that fastball ... and yet he's still less than halfway to 4K.

Coming on fast: Clayton Kershaw - (26 years old, 1,380 strikeouts) 

Kershaw will probably finish this season in the neighborhood of 1,430 strikeouts. That would rank as the eighth-highest total among all age-26 starters since 1900 (Bert Blyleven tops that list with an astonishing 1,728) and more than 200 ahead of any 4,000 Club member at the same point. Hernandez, for reference, had 1,487 K's through age 26. Like Felix, the Dodgers ace is a transcendent talent who began piling up whiffs early and has only improved with age. And like Felix, he still has a long way to go.

Too little, too late?: Justin Verlander (31 years old, 1,789 strikeouts), Cole Hamels (30, 1662), Zack Greinke (30, 1650), Tim Lincecum (30, 1638), Matt Cain (29, 1509)

The names above are basically a who's who of the last half-decade's top starters, with 18 All-Star selections, four Cy Young Awards and an MVP between them. But they all lag behind the 4,000-K pace. Ryan was nearly halfway to 5,000 strikeouts by the end of his age-30 season. Clemens (2,033) and Carlton (1,916) were also starting to pull away. Johnson's whiff total of 1,330 through age 30 would seem to provide some hope -- but he was Randy Johnson. Randy Johnson struck out 2,546 batters, which would be the 29th highest career total of all-time, after he turned 35. Randy Johnson posted the three highest single-season whiff numbers since 1975 in his age 35, 36 and 37 seasons. Randy Johnson is currently enjoying a successful second career as a professional photographer. Justin Verlander and the other gentlemen listed above are terrific pitchers. But we'll probably never see another Randy Johnson.

Hopes and dreams: Mat Latos (26 years old, 839 strikeouts), Madison Bumgarner (24, 884), Stephen Strasburg (25, 702), Chris Sale (25, 687)

Bumgarner is the most interesting of the young guns, as he'll likely finish 2014 among the top-30 all-time in career strikeouts through an age-24 season. The Giants southpaw notched his first MLB whiff at age 20 and has remained durable while increasing his K rate, but we're still a a solid decade from realistically assessing his chances at 4,000. It's also worth tossing an honorable mention to Yu Darvish, who struck out 1,250 batters in the Japan Pacific League before coming stateside. Combine that total with his MLB-best 680 K's since Opening Day 2012 and the Rangers ace would have be pushing 2,000 total strikeouts by the end of his age-27 campaign.

So, what do you think -- can any of the players listed above break the 4,000 strikeout barrier? Anyone else you'd like to nominate? Let us know in the comments or by tweeting @Cut4.