Where are you planning on fishing with it?
The 6500 holds more than enough line for clean beach work, .35mm (15 - 18lb) is plenty strong enough. The Penn won't hold that much more TBH, then again I use my 525 with 15lb line off the end of Shields pier and it does the job fine.
If you are fishing into the rocks and kelp then a Slosh 30 size with 35lb line straight through may be a better bet; you certainly won't get much 35lb line on a 6500 or a 525 for that matter.