as title says really looking to replace my door speakers would i be right in saying they are 16.5cm?

Yes but you need a set of adapters (which are plastic and crap) to keep the speaker magnet away from the window regulator or can make your own out of MDF!

http://www.caraudiodirect.co.uk/vwseat-speaker-adaptors-p-517.html?cadid=jtlfjhmm4simelgrhe82rp8hs4

I have heard of people fitting 8 inch speakers in the front door locations.

there is no point in changing it from 6.5s mine sounded awsome (jl vr650 components) and dont by adaptors just make them out of some scrap 18mm MDF, works a treat.

cheers both of you