I've just upgraded my commuter bike (old Trek 370) to the replaced components from my main road bike (originally 2009 specialized allez - new head and handle) and found the brake calipers aren't long enough (similar to this). They are unbranded calipers anyway so I'm looking to upgrade them.
Looking at these long reach calipers I've found they state
Must be used in conjunction with ST-4600, ST-4603, ST-5700, ST-5703, - ST-6700 or ST-7900 STIs for correct leverage ratio
As far as I can see these are Tiagra and above. I'm not sure which the Allez's shifters were (ST-3500?). What difference is there in lever ratio? I thought all shimano shifters were compatible and can't find any more details about compatibility.
Which calipers can I look at to work with my shifters?