We'll see! I'm 1 day in and my directly connected devices are pretty much the same as they were (34 out of 45 ish) though I realise it's early days.
Currently all RSSI's are much lower however with a number below 10. On the C7 the lowest RSSI value was 18 and the highest above 50 (I posted the results following the last Z Wave firmware update on the C7 as they improved massively at that time).
I'll give it a few days before I seek out an antenna the size of Jodrell Bank!
Edit: lowest RSSI is now 12 - I really should stop looking as it's like watching paint dry