While I think the Zard looks good and fits with the bike really well, I think the BOS and HPE downpipes look really odd going under the sump. Surely it cuts down on ground clearnce - (pavements must become a bit hazardous to say the least) and you can't put a block under the sump to lift the bike if you needed too.
For my money the Akropovic system looks and sounds the best by far.

PB rode behind me (not for long) in Hawes I reckoned the Akro sounds better than the ZARD, I couldn't say as I'm always on the bike - I think you need to be behind to get the full benefit.
Fortuntely we all have different aesthetic standards and choose the bits that suit us best. I love the fact that R12s are being modified in loads of different ways - its great. You're lucky being able to choose a can now, there have been so many fitted to various bikes that you can have a good trawl through the pics and opinions and make your choice. 12 months ago it was a bit like pining a tail on a donkey choosing a can.
I haven't seen it in the flesh but the new HPE one looks great here.
