Sucess!
I've Fixed it! ... found a crazy and extreme way of doing it, but I am now running the .423 OS with the gmail .30 Plugin, steps are below:
1.) Backup your handset using desktop manager.
2.) Make a list of all your apps, and maybe note down where you got them from (OTA URLS/App World/Desktop Install URL's)
3.) Dis-associate your Gmail account from whichever BIS system you use
4.) Remove your Sim and Memory Card from your blackberry and switch it back on so it turns on in offline mode.
5.) Wipe your handheld (Options-> Security Options-> Security Wipe-> tick both of the top boxes and wipe your blackberry clean)
6.) upgrade to the newest OS (.423) in the usual manner.
7.) insert your sim, refresh your host routing tables, and bring down all of your service books again.
8.) re-add your Gmail account (this time the message you get for installing the plugin will download the .30 version)
9.) reload your backup and re-install your apps from scratch
Yes ... this is a very long method (took me about 2 hours), and you will loose and blackberry messenger conversations and any messages in your facebook programme etc. ... but my blackberry bold 9700 is now working amazingly fast, and the gmail plugin is working brilliantely!