The OE plugs were double platinum, and the 7422 is double platinum, it's your equivalent replacement. The 6702 is only single platinum (center). It will *probably* work, but it will wear out far more quickly. It's not an awful job, but I wouldn't want to change the plugs twice as often. (I'm not sure where you got the conversion number, but it's not accurate; Bosch's own site notes the 8100 is double and the 6702 is not.)

If you want the fine wire, you'd want the 8100. I don't know anyone who has reported an issue with the 7422, though, and absent a sale or coupon deal, it's the least-expensive plug that meets OE specs.

If I may, I'd suggest testing and inspecting your plug wires as you change the plugs.

Good luck.