Thats my choice.
NOS is obvious answers ; 25 or 50bhp available. £650 for the kit, fitting can be done by myself and mates. Instant power but only on a button and the cost of refills. Must say I do like the bragging rights of "having laughing gas" though.
Unichip ; never heard of any results of this on an XE? £500 aint it?
NB. SBD 175 kit aint an option anymore ; at touching over £800 its abit out of budget, and I dont think I could really be arsed with any cold start issues ; regardless of how minor they are.