Heading up to I-10 would be a good 100 miles further than I-8. I-8 has a long uphill grade east of El Centro followed by a long downhill grade. In summer months this grade can be very hot but is fine if you travel it early morning.
I-10 route would be easier but longer. Only major grade is downhill east of Indio. High winds can occur through Banning west of Palm Springs.
Do not attempt to drive west bound on I-10 on the last day of a holiday weekend through the Palm Springs area as it can be a traffic nightmare! Otherwise its fine.