I've decided to upgrade to five lug. I have most all the pieces, so the cost will be minimal. Here's my parts checklist:

1. Struts - I have early 3" bolt spacing Boge struts.
2. Ball Joints - I need to get some pinch style ball joints ($63 each)
3. Tie Rods - I have turbo tie rods ready to go.
4. Wheel Bearings and Seals - ($20.25 per side)
5. Rotors - ($44.75 each)
6. Brake Pads - ($23.25)
7. Struts - My Koni adjustables should be reusable with this configuration.
8. Wheel Spacers for Boxster wheels - ($?)

Total cost of conversion: ~$280 + spacers