There shouldn't be a problem with you driving on Saddle Road with a rental car...

Speaking of which, I almost lost my life on Saddle Road, but that's another story. It is a windy road and can be very slippery when wet.

It takes about 2 hours drive time from Hilo to Kona... that's all about I know. For more information (excellent website with drive times) visit: http://www.ownerdirect.com/travel/dr...land-times.htm

You should be able to make it around in a day, but make it a full day plus some night time driving.

There's a lot of information on the Hawai'i board as to what the best sites are on the Big Island. Thus, a search would warrant some good information

Hope this helps! Aloha