gistfile1.cs

// type your offers.xml path
var xmlUrlOrPath = @"D:\Work\parfumstudio\Exchange\offers_2014-10-10T02-08-30.xml";
var doc = XDocument.Load(xmlUrlOrPath);
// parse xml
var offers = doc.Descendants("Предложение")
 .Where(o => o.Element("Штрихкод") != null)
 //.Skip(400)
 //.Take(15)
 .Select(o => new {
  SKU =  o.Element("Штрихкод").Value,
  Name = o.Element("Наименование").Value,
  Price = decimal.Parse(o.Descendants("ЦенаЗаЕдиницу").First().Value.Trim(), System.Globalization.CultureInfo.InvariantCulture),
  Stock = int.Parse(o.Element("Количество").Value)
 });
//offers.Dump(); 
var offersSKU = offers.Select(o=>o.SKU).Distinct();
var part = 2000;
var cycles = (int)Math.Ceiling(offersSKU.Count()/(double)part);

for(var i = 0; i < cycles; i++ ){
 // get variants that corespondend parsed from xml offers
 var partOffers = offersSKU.Skip(i * part).Take(part);
  var variants = Variants.Where(v => partOffers.Contains(v.SKU.Trim())).ToList();
 
 var variantChanges = variants
  .GroupBy(v=>offers.FirstOrDefault(o=>o.SKU==v.SKU.Trim()))
  .Where(vg=>vg.Key != null)
  .SelectMany(vg => vg.Select(v=>new{
   Product = v.Product,
   Variant = v,
   vg.Key.SKU,
   //ProductName = v.Product.Name,
   VariantName = v.Name,
   SitePrice = v.Price,
   DbPrice = vg.Key.Price,
   SiteAvailability = v.Availability,
   DbAvailability = vg.Key.Stock > 0,
   SiteStock = v.Stock,
   DbStock = vg.Key.Stock,
   //Url = "http://parfumstudio.ua/shop/" + v.Product.Url + ".html",
   EditUrl = "http://parfumstudio.ua/admin/product/edit/" + v.Product.Id,
  }))
  // uncomment if want to show onlu changed variants
  .Where(v=> v.DbPrice != v.SitePrice || v.DbAvailability != v.SiteAvailability)
  .OrderBy(v=>v.Variant.ProductId)
  ;
 // output variantChanges
 variantChanges.Dump();
 
 foreach(var change in variantChanges.Where(v=> v.DbPrice != v.SitePrice || v.DbAvailability != v.SiteAvailability)){
  change.Product.Visible = change.DbAvailability;
  change.Variant.Price = change.DbPrice;
  change.Variant.Availability = change.DbAvailability;
  change.Variant.Stock = change.DbStock;
 }
 // Uncomment to submit changes
 SubmitChanges();
}