Not much difference at all. Both good, almost identical specs.
BUT, according to bushhog the 297 is a discontinued model, and the BH27 is the replacement. Also has nearly identical specs. Might be some incentive to get a better deal on the 297.
If I were you though, I'd overlook the 7' single spindle cutters and look to an 8' twin. You tractor will handle it better. Something like a BH2008 ro LP2596. You give up some cut capacity, but once the first mowing is done, as long as you keep it maintained there is no need for a heavier duty cutter unless you plan on cutting commercially IMO