There is a difference. The original S2 had better GPU the S2 PLUS not only has different GPU the processor is also different.
In terms of performance the Original S2 is much much better.
S2 PLUS I9105
[TABLE="width: 1"]
[TR]
[TD="class: ttl, bgcolor: #FAFAFA"]Chipset[/TD]
[TD="class: nfo, bgcolor: #FAFAFA"]Broadcom BC28155[/TD]
[/TR]
[TR]
[TD="class: ttl, bgcolor: #FAFAFA"]CPU[/TD]
[TD="class: nfo, bgcolor: #FAFAFA"]Dual-core 1.2 GHz[/TD]
[/TR]
[TR]
[TD="class: ttl, bgcolor: #FAFAFA"]GPU[/TD]
[TD="class: nfo, bgcolor: #FAFAFA"]Broadcom VideoCore IV[/TD]
[/TR]
[/TABLE]
S2 I9100
[TABLE="width: 1"]
[TR]
[TD="class: ttl, bgcolor: #FAFAFA"]Chipset[/TD]
[TD="class: nfo, bgcolor: #FAFAFA"]Exynos[/TD]
[/TR]
[TR]
[TD="class: ttl, bgcolor: #FAFAFA"]CPU[/TD]
[TD="class: nfo, bgcolor: #FAFAFA"]Dual-core 1.2 GHz Cortex-A9[/TD]
[/TR]
[TR]
[TD="class: ttl, bgcolor: #FAFAFA"]GPU[/TD]
[TD="class: nfo, bgcolor: #FAFAFA"]Mali-400MP
[/TD]
[/TR]
[/TABLE]