Same code ran noticeably slower when compiled in D2. Just because a program goes from 16 to 32 bits doesn't imply a speed increase - sometimes it means a speed decrease. If you want a real shock, try running an 8-bit program on a pentium sometime. No way to answer this question without a first-hand analysis of the code. I'd suggest running it through a profiler if you have one, maybe you'll find a bottleneck that way.
Streams are fast.
I wouldn't expect RTTI to be necessarily fast, depending on what you're using it for. BC5 is over four years old. BCB4 is a little more than a year old. I'd expect a difference. Three years is an eternity in this business.