I run a 60" KKII on my 26.5 PTO HP
L3240 and the only time I have bogged it down was in heavy, wet clay that loaded up the spool & added about 300 lbs to the tiller. BTW, the PTO clutch is a nice feature of this tiller and it's included in the price.
A lot of the HP requirement goes to keeping the tines spinning at 540 PTO speed in your slowest forward gear. This is an area where I think the HST has a distinct advantage as you can crawl at as slow a speed as you need to keep the spool spinning at the desired rpm. My tractor is gear drive and the first gear ratio limits how slowly I can move at 540 PTO speed (about 0.9 mph). As a result, when I'm in the heavy clay I need all of that power.
With the 2920 I would carefully assess minimum forward speed at 540 PTO speed as well as PTO HP before making a decision to buy.
-Jim