M_V's multitude of bikes and adventures in the land of framebuilding

Really? I thought the spacing was different? I guess it wouldn't be coz 7 to 8 speed was where the width changed.

Yup, you got it, the width have changed.

5/6 speed have the same spacing (5.5mm), this is where you got the loveliest "clunk" sound when you change gear.

7/8 is 0.5mm closer at 5.0mm, then a massive drop to 4.34 when you head toward 9 speed.

8 speed are cheap as chip nowadays, what you can do is set the screw limiter correctly for the 8 speed width, and then indexed the shifter to the smallest to the second biggest cog.

When you need that 8th cog, simply switch to friction and shift up, basically the slowest index shift ever, but it mean you get to use your 7 speed shifter fully on an 8 speed cassette without buying a new shifter.

It could also be a useful way to force you not to cross-chain.

Oh and I took your advice and have just bought a couple stainless cages off ebay so one can go under the downtube.

Good call, alu bottle cage are light but fragile, they're definitely not used to the constant removing/installing of the bottle cages, which tend to get a little loose over time.

When it's upside down, I found the weight of the bottle made the cage a lots looser than it should, after 113 miles, the bottle was rattling away ready to be jettison toward the front wheel for it's final oblivion, it was good fortune I found out then before heading onto a very long tour with a steel cages instead.