I agree with both of the previous posters (!) - 8 strings will definitely give you more versatility than 6, and having the high G and D will give you loads of options for
both kinds of music*
I got rid of a couple of lap steels to get a pedal steel, and although I would never now get rid of the pedal steel, I do miss the lap steel a lot.
I have tried to play a bit of rockabilly on the C6 neck, and found I really miss the top G. Not the end of the world, but it means a lot more horizontal movement - so a lighter bar is definitely preferable!
Maybe one day, when I have some more spare cash I shall get another plank. Though I may also have to find some more hiding places around the house for the other guitars too...
Good luck with lap steel, Mathew - your pedal steel playing is exceptional, and I really look forward to hearing you on lap steel.
Best regards,
Sid
*That's Country and Western, as I think you may be of a generation born long after 'The Blues Brothers'
