You answered the question - Shimano 2300 8spd rear mech. Also, Shimano's Acera or Alivio versions have longer cages to accommodate bigger toothed 8 speed cassettes (some cyclo cross bikes mesh 2300 road components with Alivio MTB parts). All work well and there is little scope for upgrade, as none is needed.
or if you have the budget and the balls to take on a project, you could strip out your entire chainset and go for a 9spd tiagra or 10spd 105 kit........
All depends on your budget and just how mental you want to go in the process... If you love the frame and it fits you well, a significant upgrade would be tiagra for the most quim for quid.
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All depends on your budget and just how mental you want to go in the process... If you love the frame and it fits you well, a significant upgrade would be tiagra for the most quim for quid.
If so, any Shimano 8 or 9sp long-cage road rear mech will be fine : 2300, Sora or Tiagra
Don't go for 10speed, it'd work but be a waste of money
A 8 or 9sp MTB rear mech would work too, but isn't necessary with just 12-26 : you just don't want a short-cage road one with your triple.