You know, in reading all these threads, there is no right or wrong path here. Yes, how well you can ride is a big factor. And yes a pure road bike with a race fast rider will cream all the other alternatives. But that's not the issue that was raised in June. The original thread wanted to combine a faster bike than a mountain bike to better keep up with his riding partner/brohter. The three answers that I see on these threads will all guaranteed, provide what the original thread requested;
1. to better keep up with his brother's Trek 7.2 Fx Hybrid (a road oriented hybrid at that)
2. A bit of pedaling challenge to be left in the equation to help improve fitness (as opposed to I assume a pure race road bike)
3. Something that would better take the pounding of poor roads
I would suggest that any of these would work
1. 26" Mtb with slick thin tires
2. a cylcocross bike
3. a 29er with slicks.
So whatever floats your boat and can gets the most use. I got to my Jamis Dragon pretty much by accident and have just made good use of it. It allows me a single bike on road trips so that if I find roadies, Im OK or go mtb riding. But a cyclocross bike might do it great for me too. Or a 29er with slicks. Lets face it, if you're on this BF, you love to ride and most of the time enjoy the heck out of it whichever bike you're on.
By the way your brother's Trek 7.2 FX IS a 29er with slicks. These are 700cc wheels, really the same as a 29er's and he has relatively narrow road oriented tires.
Someone chimed in about speeds above 28mph - hardly relevant in this conversation unless we are going downhill. And the somewhat arrogant comments about levels of knowledge and bike fitness also not that relevant. The point is what makes THIS rider faster than a 26" Mtb bike to better keep up with his brother. And all of the above do so and nicely.
I can do paceline in the mid 20's with my Jamis Dragon/1.5 Kenda Kwests, though as mentioned its a bit of extra effort, mostly because I don't have the upper gears once moving. And that Jamis Dragon mtb bike is race frame, skinnier smooth tires, shorter cranks and a bunch of lower gears, accelerates better than my Scott CR-1 carbon fiber road bike. And toe to toe with my riding compadres I can keep up or slightly outspin most them in a sprint for brief periods. The going gets tougher over distance - hence my comment about taking a little more draft time than I might othewise (but I still take turns pulling).
So, they're all good and in fact I get so much pleasure and use from all the bikes I own (4), it becomes obvious - biking on almost anything is great and if you do it enough, you will get fit enough to make all the kinds of bikes out there fun.
By the way, I also a have a 29er (Titus Racer X 29er) and thought about slicks or semi slicks for it - but can't find them anywhere. Has anybody seen them any anywhere?