The memory bandwidth will be exactly the same. It's calculated as (Effective Memory Speed x Bus Width)/8. These numbers are theoretical rather than benchmark proven, but I think all manufacturers do the same thing.
So (1600mhz x 128bit) = 204800
204800 / 8 = 25600 MBps or 25.6 GBps
The GT630 is not great in the price/performance stakes, and really is only a modest performance upgrade from a HD4670. By this I mean although it's cheap to buy, the performance you are buying per $ is not great. A little up the price range is where manufacturers really compete. For example, a GTX 750 (non Ti) has a street price starting from about $100-$110 in the US compared to (I'm guessing) $60-70 for a Gigabyte GT 630. However, with no exaggeration, the GTX 750 performs approximately 4 x faster overall than the GT 630. AMD's R7 260X is not far behind, and in a similar price bracket to the GTX 750. Personally I would try to find the extra $40 for 4 x the performance, even if it meant holding off for a month or two.
If the extra cost is just not an option then there are deals like this R7 260X at $70 (however part of that price is made up of a mail in rebate). For a clean price with no mail in rebates etc as close to the price of the GT 630 as possible, there's (for example) this GT 640 but there aren't many options at this price level. It's not in the same league as the GTX 750 or R7 260X by a long way. But it does at least feature GDDR5 memory and overclocked GPU and should perform better than the GT 630 DDR3 by about 50%. A 'trick' at the low end of the GPU market is to offer models hampered with slower memory (DDR2 or DDR3) at cheap prices while the samples sent out initially to review sites get fast GDDR5... Always check what memory is used in any prospective purchase and if DDR3, look to see if a GDDR5 version is available for similar money. GPU's really benefit from higher memory bandwidth..