May I also suggest that you invest in a banquette for the one solid wall? that will gain you at least 2' of pulling the chair out space . . see the options at ballard / cover it with sunbrella - fill the entire wall with it and let the table be smaller so people can sit and slide in . .

The largest free-standing table that will comfortably fit into your space is one that is 3' x6'. If you choose to have a banquette built in, you may be able to use a slightly wider table. Your only real choice for shape is a rectangular table.

I once had a table with over rather than square edges on the ends that adjusted from a table intended to seat four to a table that would comfortably seat six by using two foot wide leaves -- extender pieces -- that you added to the middle of the table after pulling the two ends apart.

You might be able to find an oval or rectangle table that is a drop leaf table.

Do you need to seat more people on a daily basis or just on special occasions?

If you had two 28" square tables, you'd be able to use one for daily use but be able to put the two of them side by side when needed -- relegate one to a corner of another room when not needed or, with legs taken off, stored under in a closet or under your bed.

If your budget is really seriously as tight as is your space, and if you are willing to think outside the box and be a bit quirky with your decor and really need to be able to seat more people but only on special occasions rather than on a daily basis, and IF your current table base is strong enough to handle the weight (or you're willing to invest in one that is), there is something else you might consider. You could get creative and make a second, larger, table top for your base either as one fixed 3'x6' piece which would hang it on the wall of your dining area or be stored under a bed when not in use as a dining table top, using the smoother plywood intended to be finished and seen or, alternately, use three pieces with hinges to create a folding top that could be stored either in a closet or under a bed.

If there is a used office furniture store or a Habitat for Humanity Restore Store or an antique/used furniture store near you, check them out as you look for an alternative to your current table that will not bust your budget.

Painted with exterior black paint, your current table base likely could be used on the deck or patio to which the patio doors lead, preferably storing the glass top inside when not actually in use.

Thank you for your comments. I don't need to seat more than 4 ppl in daily basis... so I would extend the table only in special occasions (3-4 times/yr)... so I wonder if I should buy same size table of what I have now. Sofibebe, actually one of my options are Bjursta series in Ikea, they are extendable either round table (same size as what I have, to be extended 20" to oval ) or rectangular (33" W X 55" L to be extended up to 86" L).

Here is the other table from cb2

http://m.cb2.com/core-black-extension-dining-table/s322128

Ikea gets a bad rap sometimes, but i find they have some really good solutions to a lot of space issues, a little bit more contemporary with some of their lines, and overall just less hulky/bulky furniture.