You are SOOO in luck 
The new A608 will be out soon, which is a PCMCIA-friendly 8MB Fast RAM expansion for the A600 which fits nicely at the same time as the A603. If you use a PCMCIA card, like a CF-reader or Ethernet adapter, the RAM will be reduced to 5.5MB, which is a limitation of the A600 design, but this is better than 4MB! Of course, once you've got the A603 and A608 in there, you can also fit an Indivision ECS, a ROM switcher and 3.1 ROMs, and maybe an MP3@64 or Subway USB on the Clockport.
The A600 is suddenly becoming expandable!
Here's a link to the forum where you can put your name down for an A608 - http://www.a608-amiga.co.uk/
10MB A600s rock for WHDLoad games!
yes! I own one of those mighty 8MB russian expansion and it's great! :-) Since it's going to be produced again in the UK it's a good chance to get one.
