As a trackie I've owned (and currently own, sadly) every size of Kreitler plus TruTrainers and every other kind of roller out there. A few comments.
First, rollers are best for developing strength and aerobic capacity at high rpms. Don't limit yourself to 100 rpm. The aerobic capacity totally carries over from riding 160 rpm to lower cadences, and if you're really trying to build power, you probably want to consider plyometrics or free weights over rollers or trainers anyway.
Second, among Kreitlers, the headwind trainer does provide a lot of resistance with the cover on the side closed, but in my own opinion it's noisy, klutzy, and makes your roller assembly quite long and a pain to assemble and disassemble each time you ride. If you have a place where it can just sit out, this isn't as big a problem, but if you want to use it in a doorway watching tv, it can just become the difference between training and saying that the assembly is too much. I also find that it's a bit erratic and for trainer training, you really want something very reproducible and consistent.
Kreitler also has some flywheel weights, but I don't recommend them at all. They are poorly made and I've never seen ones that are perfectly round, so they create a vibration in the rollers and simply don't roll smoothly.
Let me say that if you want high wattage outputs on rollers, you should be looking at TruTrainers (www.trutrainer.com
) with the flywheel option. Nothing but nothing gives the same degree of smoothness at higher resistance, and you can get the release option so you can disengage the internal flywheel and use them for more of a spinning ride. They are pricey and heavy, but they fold (which eMotions don't) and once you're used to rollers you really don't need all the hardware on eMotions. I'll say that I see a lot of eMotions up for sale from people who are changing to other simpler rollers, but rarely see TruTrainers for sale.
In Kreitlers, you can get two frame designs, the Kompact (where the drums bolt into holes on a flange on top of the frame and have to be unbolted to move) and the Classic (where the drums can slide back and forth with the release of a quickpin. The advantages of the Classic are that you can get ultra-short or long wheelbases with them, and you can adjust wheelbase easily. However, the pins tend to fall loose and everything is more susceptible to rattling and feels less rigid. The Kompact comes standard with 3.0 inch drums, but you can put any drums on it you want. They don't fold up as compactly with 4.5 inch drums for some wheelbases, that's all. With 3.0 drums, everything works fine for road bikes, and with 2.25 drums, you can do anything with them.
As for choice of drum size, the 2.25 drums basically cause the tire to flex more radically, thus creating more resistance. The feeling is akin to riding tires with very high rolling resistance. It's good training but unless you pump up your tires a bit more (which then reduces wattage max) you don't feel as much snap in your accelerations on this size drum. I do like riding them just for a really tough workout, but not for daily riding (which for me, as a track rider, involves more high cadence workouts where that sluggishness is actually counterproductive to my training). The 3.0 inch drums are a good compromise. I can't say I'm overwhelmed by the feeling, but they're certainly lighter, more compact, and, as I said, a good compromise.
My point is, don't write off the 4.5 inch drums. You can get a hellacious workout on them at higher cadence, which is what they're really best for anyway. Then do plyometrics, stair jumping, free weights, whatever you want to build power. It's more focused and more effective for winter improvement than simply riding a trainer or riding rollers with resistance.
And by the way, don't reduce your tire pressure or put a towel under one roller to increase resistance. Both approaches are often suggested, but not wisely. Lower tire pressure can make you prone to a blowout plus it just takes away the snap from your accelerations. And the towel is an invitation to having something snag, at which point you usually go down. It's also completely lacking in reproducibility and consistency.