Then you don't want the SP2 since its charging setup would be similar to the SP3.
In terms of performance (and everything really), the SP3 is a better device than the Dell Venue 8 and Venue 8 Pro. It has a more powerful CPU, more powerful integrated graphics, faster RAM, an SSD instead of eMMC (SSDs are faster), a larger display at a higher resolution, a very capable Pen, etc. But it also starts out at 4X the cost of the Venue 8 Pro and it's not fair to compare an $800 system (actually $950 with the keyboard cover) to an 8" Windows tablet at $200.
The Surface 3 is more expensive than the Venue 8 Pro as well and pretty much offers all of the same benefits as the SP3 (Surface Pro 3). It has a faster CPU, more powerful graphics, a larger display that is higher in resolution, faster RAM, faster eMMC storage, better battery life, and supports a Pen. They are really in two different categories as the Atom x7 SoC in the Surface 3 is above and beyond the Atom SoC in the Venue 8 Pro both in terms of CPU and integrated graphics performance. Either one is an upgrade over the Venue 8 Pro but then again, they are both a lot more expensive than the Venue 8 Pro (which is a really good 8" Windows tablet).