First, you should understand that IEMs v. Full-size headphones are totally different listening experiences. Full-size headphones will give you a much better sense of "space", they will probably cast a slightly more honest soundstage, and they are likely to have more visceral bass because they'll be moving a lot of air at your ears. They will get you one step closer to (but still very different from!) what a speaker setup would sound like, especially if they are open air.
BUT - Coming from JH-13s, I agree with the above poster that you are unlikely to find the sound quality of full-size headphones comparable or superior to your IEMs unless you spend a lot of money - I know of many people that have decided to do away with their full size rigs entirely because the JH13 sounded so good and was so much more compact than a full desktop amplifier, etc. So the most important thing is setting expectations - no low- or mid-tier full size headphone will come close to the JH13 in terms of neutrality, detail retrieval, and speed.
Regarding the headphones you mentioned - as the above poster said, I think the HD650 will not serve you well. It's darker than the JH13, and has a "veiled" quality that a number of people (including myself) don't like, which I think will be even more pronounced if you are used to listening through IEMs (which are often very detailed and fast when they use balanced armatures). I've never been a huge fan of any of the Grados myself - they never sound quite right to me and I find them unforgivably uncomfortable, but of course there is a wide range of opinions on them.
The last thing you should of course note is that for many full sized headphones, to get performance comparable to what you hear out of your JH13s will probably require some investment in good amplification as well, which isn't cheap, and once you have a nice big desktop amp, you'll want to buy a new DAC, cables, etc. etc. etc.
I think you have three choices:
1) Keep your JH13s and be content with them, and don't buy anything else
2) Buy a pair of full size open-air headphones that are reasonably priced with a reputation for relative neutrality, but go into it with the expectation that you are buying the headphones to get a different "type" of listening experience, with more soundstage, air, more visceral bass, etc., but that you will NOT necessarily be getting a more "technically proficient" reproduction of sound. Some good choices here might be an HD600, K701/2, DT880 or AD2000 (slightly pricier), depending on which ones sound from reviews that they will best match your listening preferences. If you can get your hands on a vintage Stax setup (Lambda + amp) for ~$500, that would be my personal recommendation (as I think it would actually sound better than your JH13s in some areas)
3) Get yourself a proper high-end rig that will actually be able to compete technically with your JH13s, but be prepared to spend somewhere in the range of $1,500-$2,000 (or more!) to accomplish this. LCD-2 + Schitt Lyr, for example.
Good luck!
