Here's my L2500 string journey so far:
I tried EB Cobalt flats for a week or so, and they sound fat as hell, sound great, but not quite enough high end bite for me. Also, the G and D are much brighter than the other strings, although that might wear off.
Yesterday I put on a set of GHS Pressurewounds. They are a bit brighter although not hugely so. The top 4 strings sound quite good, even though they don't have the hifi pristine highs of true roundwounds. But… the low B is kind of ick. It is huge but very dead sounding, not like the other strings, actually deader than the Cobalt flat B. It doesn't feel like the string is bad, just maybe doesn't match the bass or my touch or whatever.
The sound of the low B is important to me, so that's kind of a deal breaker unless is miraculously improves in the next day or so. Next on the block: my current top roundwounds, DR Nickel Lo-Riders.