Don't think the Jag will be lighter - our XJ40 XJR that had the 6 Cylinder lump weighed in at something around 1700kgs.
The X308's also suffered from the dreaded tin worm as well, the unit's had numerous revisions of the timing chain tensioners as they tend to go through them like hotcakes too...
If you're looking at a Jag, either go for a late X308 V8 - 2002 onwards, however they tend to be pricey. Personally I'd go for the earlier (X300) which featured the Supercharged 4.0 6 Cylidner, 324bhp and it's a bullet proof engine.)
However, if you're wanting a V8 toy, This is what you want.....http://cgi.ebay.co.uk/2001-51-BMW-M5-PR ... 013wt_1139
400bhp without any form of super/turbo charging.
6 speed manual (no auto available!)
Usable as an every day car if needs be, no rust (unless it's been shunted!)
Voted one of the best generations of 5 series ever produced...